Men with neurotic personality traits, such as moodiness, were also found to have fewer children compared to previous generations. The study used survey and birth registry data on more than 7,000 Norwegians from 1927 to 1968.

While the study is based on subjects in Norway, head researcher Vegard Skirbekk says that the findings likely apply more widely. "Norway is a leader country in terms of family dynamics," he said. "Many trends that have been observed first in Norway -- increasing cohabitation, divorce rates, and later marriage, for example -- have then been observed later in many other parts of the world. Of course it remains to be seen if this phenomenon will also spread."

The research follows a 2010 study from the UK's University of Sheffield that found that in societies with high birth rates, neurotic women and extroverted men are likely to have more children. That study was published in the journal Proceedings of the National Academy of Sciences.

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